\cleardoublepage ends the page, prints out remaining floats if necessary, and ensures that the following text starts on a right hand page, as chapters in books commonly do, if in twoside mode. \clearpage, in contrast, would start the new page on a left or a right side.

\phantomsection is a command of the hyperref package, which creates an anchor at this location, similar to \hypertarge, which can be referred to - \addcontentsline does it implicitely. Without \phantomsection, \addcontentsline would refer to the previous anchor which could be undesired.

The package tocbibind makes putting commonly added chapters/sections (bibliography, TOC, index) to the TOC easier. It's integrated in the memoir class, while KOMA-Script classes support this purpose by class options such as bibliography=totoc.